Many articles made from sheet materials are composed of parts containing different materials, each material being desirably present to impart one or more specific properties to the article. For example, housings for electronic or electric components may comprise an electrically insulating part for electrically isolating the component it houses and an electrically conducting part for shielding or for making a desired electrical connection. Small anti-friction bearings often have a structural part for transferring the forces of the journaled part to a mounting and an anti-friction part carried by the structural part for engaging and carrying the journaled part. Frequently, an article composed of two or more materials is made by assembling it from separate parts, each of which is made exclusively of the appropriate material. Another way of making such an article is to make one part and then coating, casting, or molding the other part in situ on the first part. Occasionally, a two-material article is made from a laminate of the two materials by first shaping the article and then removing one material from selected zones.
The manufacture of insulating or shielding housings for electric or electronic components provides a good example of the state of the art. At one time, almost all such articles were made by assembling separately produced conductive parts and non-conductive parts. Even now, most ordinary light bulb sockets have an inner conductive sleeve into which the bulb is screwed and a separate outer insulating sleeve that telescopically receives the conductive part. Shields for electronic components, such as IF cans and transistor housings, are now usually made by either forming a cup-like member of conductive material and spraying or otherwise applying an insulating coating on the inside of the can or by forming the cup-like member from a laminate of a conducting material and an insulating material and then removing the insulating material from the solder lugs. Various articles of two or more materials may also be made by first producing individual blanks composed of a substrate sheet and then adding a selective coating (or coatings) of another material printed, deposited with a screen or stencil or otherwise formed in desired zones.
The techniques described above, though adequate as far as achieving a desired end product is concerned, are relatively complicated and costly. The tooling and labor involved in making separate parts and then assembling them, in casting or coating in situ on formed parts, in selectively removing material or in making and processing individual blanks adds greatly to the time, costs and quality control problems involved in a production operation, as compared with the manufacture of a single part of one material.